The present invention is directed to improvements in lift truck load clamps, of either the sliding or pivoted-arm type, for handling large rolls of paper such as newsprint and kraft paper.
Such clamps are normally required to handle paper rolls of widely-varying diameters in both vertical and horizontal orientations. A typical clamp comprises a pair of clamp arms either slidably or pivotally mounted upon a clamp frame and movable with respect to such frame selectively toward and away from each other to engage or release paper rolls of different diameters. Each clamp arm normally has a concave contact pad on the forwardly-extending tip thereof for engaging the cylindrical surface of the roll. For proper engagement, to ensure that the roll does not slip from the grasp of the clamp, it is important that the two contact pads engage the roll in substantially diametrically-opposed positions. This requires the lift truck operator to adjust the positions of the clamp arms relative to the roll prior to engagement such that the contact pads will neither underreach nor overreach the roll but rather will engage it in such diametrically-opposed positions. Because lift truck operators are normally hampered by visibility limitations imposed by the lift truck mast and clamp frame, it is often quite difficult for the operator to see the exact relationship between the contact pads and the roll. Particularly when rolls of different diameters are being handled, the operator is often forced to estimate roughly the proper positions of the contact pads with respect to a particular roll, resulting in inaccurate positioning of the contact pads and insecure engagement of the roll.
A solution to this problem has been proposed in Frischmann et al U.S. Pat. No. 2,596,477 which shows a paper roll clamp having a single pivoted clamp arm of substantial length and a fixed shorter clamp arm. The clamp includes an elongate load positioner having one end connected by a toggle and link assembly to the pivoted clamp arm so as to move forward automatically in response to closure of the pivoted clamp arm and move rearwardly automatically in response to opening thereof. The purpose is to ensure diametrically-opposed gripping of paper rolls of different diameters by the contact pads.
However, because the opposite end of the positioner is affixed pivotally to the clamp frame, the positioner is operable only with respect to a clamp having a single clamp arm movable with respect to the clamp frame. The positioner is not, for example, operative with respect to a clamp wherein both clamp arms are movable with respect to the clamp frame selectively toward and away from each other, or with respect to a clamp wherein both clamp arms are movable in unison transversely with respect to the clamp frame so as to handle a particular paper roll in different transverse positions.
Modern paper roll clamps such as those shown in U.S. Pat. Nos. 3,896,957 and 4,127,205, require movement of both clamp arms toward and away from each other relative to the clamp frame primarily to be able to handle small as well as large diameter rolls in a substantially centered position relative to the axis of rotation of the clamp rotator. Substantial centering of rolls of different diameters enables the rolls, when rotated to a vertical orientation, to be inserted into or extracted from an array of vertical paper rolls in close proximity to one another by permitting the clamp arms to slip between the closely adjacent rolls without damaging the fragile surfaces thereof.
The further ability of both clamp arms to be shifted transversely in unison with respect to the clamp frame is primarily needed to enable the clamp arms to engage a given paper roll both in a position of unequal extension, wherein the forward end of one clamp arm extends a greater distance forwardly of the lift truck than the forward end of the other clamp arm and, alternatively, in a position of equal extension wherein the forward ends of the clamp arms on either side of the paper roll extend a substantially equal distance forwardly of the lift truck. The unequal extension position is needed when a paper roll is lying in a horizontal orientation on the floor or other supporting surface, so that the upper clamp arm can overreach the lower clamp arm in order to assume substantially diametrically-opposed positions for grasping the roll firmly. Thereafter, if the paper roll is to be stacked vertically by rotating the clamp about its axis of rotation, the equal extension position is desirable to facilitate handling of the roll in close proximity to other vertically-oriented rolls.
In the aforementioned Frischmann et al clamp, if both of the clamp arms were movable with respect to the clamp frame, the load positioner's relationship to the clamp arms for diametrically-opposed roll engagement would change and thus become inoperative upon movement of the fixed clamp arm with respect to the clamp frame. This is because one end of the Frischmann et al load positioner is pivotally fixed to the clamp frame and therefore is not movable in response to the movement of the clamp arms toward and away from each other. The same problem would exist if the Frischmann et al clamp arms were capable of transverse movement in unison with respect to the clamp frame, since the fixed pivotal connection of one end of the load positioner with respect to the clamp frame would prevent the positioner from moving transversely in unison with the two clamp arms.
Other types of clamps having various load bumpers or positioners for loads of differing dimensions are shown in Russian Pat. No. 197,709, German published patent application No. 28 35 447, and U.S. Pat. Nos. 2,959,310 and 3,371,952. However none of these provide suitable solutions to the problems of paper roll clamps discussed above. Moreover such prior load positioners are inflexible and thus not conformable to cylindrical roll surfaces of different diameters, permitting relatively high impact stress when the lift truck is advanced forwardly into engagement between the load positioner and the load. This condition can cause excessive bearing force against the fragile paper roll surface and resultant costly damage to the outer layers of paper.
Accordingly what is needed is an automatically adjustable roll positioner, preferably of flexible construction, for ensuring diametrically-opposed engagement of paper rolls of different diameters which is operative with clamps wherein both clamp arms are movable with respect to a clamp frame, and wherein the clamp arms are movable transversely in unison with respect to the clamp frame.